1. Field
The present invention is a fermentative process for manufacturing xylanase-rich enzyme complexes. Pre-treated thin stillage of rye acts as an inductor for xylanase formation.
2. Description
Xylanase is a hemicellulase enzyme which hydrolyzes xylans (also called "wood gums") to xylose and other sugars. The enzyme is also known as endo-1,4-.beta.-D-xylanase or 1,4-.beta.-D-xylan xylanohydrolase and belongs to the EC 3.2.1.8 enzyme class. Xylans are polysaccarides formed from 1,4-.beta.-glycoside-linked D-xylopyranoses with short side-chains of different composition, and can contain arabinose, glucose, galactose and/or glucuronic acid as well as acetyl and methyl groups in the molecule. Xylans are components of many deciduous and coniferous trees, as well as cereals, bran, pectin, tragacanth, plant gums, etc. Xylans are structurally diverse. Therefore, complete degradation of branched, partially acetylated xylans requires the action of a variety of xylanases to hydrolyze the xylans to xylose and other sugars. The mode of action of xylanases is complex and is realized in conjunction with other (to some extent synergistic) enzymes.
Xylanases are formed by fungi (for example, Trichoderma, Penicillium, Aspergillus, Talaromyces and Sporotrichum) and bacteria (for example, Clostridium, Cellulomonas, Bacillus, Thermononspora and Ruminococcus). Xylanases are used in the cellulose industry as bleaching and improving agents, and have been recently utilized in the manufacture of animal feed. Studies indicate that exogenous enzymes, such as xylanases, added to animal feeds containing rye, barley or triticale (1) favorably reduce the antinutritive action of the non-starch polysaccharides and (2) improve digestibility and absorption of the nutrients in the intestine of the animal. The most important enzymes (used extensively in broiler rearing) can hydrolyze the non-starch polysaccharides present in cereal types such as, barley, wheat, and rye. Several preparations containing such enzymes are already on the market. For example, Roxazyme.RTM. G (Roche) contains cellulase, .beta.-glucanase, and xylanase. Such preparations are admixed with the animal feed to achieve the mentioned advantages. Xylanase-rich enzyme complexes manufactured in accordance with the subject invention are useful for producing these preparations. The use of xylanase as a feed additive in poultry nutrition is an important application. Substantially increased nutritive value of broiler feed can be achieved with energy-poor cereal types, such as barley, oats, rye, and triticale [see Mh. Vet.-Med. 48: 213-217 (1993) and the references cited therein].
Attempts have been made to selectively increase the xylanolytic activity of xylanase producing microorganisms. Xylan-containing substances have been added to nutrient medium (fermentation medium) to induce xylanase formation. Purified xylans, wheat bran, barley glume, milled maize cobs (maize spindle flour), straw, and thin stillage of rye are examples of these substances. By such means it is possible to increase xylanase activity [see as technological background German Patent Specifications DD 278 359 and DD 291 673; European Patent Publication (EP) 0 455 928 A1; Appl. Microbiol. Biotechnol., 40: 224-229 (1993); and Enzyme & Microb. Technol., 18: 495-501 (1996)]. This inductor effect can be achieved in a cost-effective manner using thin stillage of rye. Unfortunately, however, increasing concentrations of thin stillage of rye inhibits the growth and enzyme formation of the described microorganisms.
The present invention provides a process for manufacturing xylanase-rich enzyme complexes using cost effective thin stillage of rye.